The invention relates to a hydrodynamic control coupling of the type whose axis of rotation is normally vertical and which includes a primary vane wheel or impeller and a secondary impeller which, together, form a toroidal working chamber. The coupling further includes a shell-like enclosure which rotates together with one of the impellers while enclosing the other. The coupling is further provided with a drainage means through which the working fluid may pass from the working chamber within the impellers to a locally fixed storage container and the system further includes a supply conduit which leads from the storage container via a control valve into a region lying immediately below the lower impeller. A known coupling of this type of construction (illustrated in the hand book: "VOITH Hydrodynamische Getriebe, Kupplungen und Bremsen", published by Otto Krauskopf Verlag, Mainz, Germany, 1970, page 256. Also illustrated in VOITH Company publication G 596, illustration 5) discloses a low lying storage container for the working fluid. The drainage means for the working fluid from the working volume into the storage container is located beneath the working chamber and is embodied as a fixedly attached scoop tube. The supply conduit, which serves to take working fluid back into the working chamber, includes a pump driven by the shaft of the primary impeller and a pressure line through which the fluid medium is passed through a control valve into the working chamber. The degree of filling within the working chamber, and hence the r.p.m. of the secondary impeller, can be adjusted by adjusting the control valve. The control valve may be adjusted by a regulating mechanism in dependence on any suitable parameter, for example a temperature (if the coupling drives a fan) or of a pressure (if the coupling is driving a pump).